/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.log4j.helpers;

import org.apache.log4j.spi.LoggingEvent;

/**
 * CyclicBuffer is used by other appenders to hold {@link LoggingEvent
 * LoggingEvents} for immediate or differed display.
 * 
 * <p>
 * This buffer gives read access to any element in the buffer not just the first
 * or last element.
 * 
 * @author Ceki G&uuml;lc&uuml;
 * @since 0.9.0
 */
public class CyclicBuffer {

	LoggingEvent[] ea;
	int first;
	int last;
	int numElems;
	int maxSize;

	/**
	 * Instantiate a new CyclicBuffer of at most <code>maxSize</code> events.
	 * 
	 * The <code>maxSize</code> argument must a positive integer.
	 * 
	 * @param maxSize
	 *            The maximum number of elements in the buffer.
	 */
	public CyclicBuffer(int maxSize) throws IllegalArgumentException {
		if (maxSize < 1) {
			throw new IllegalArgumentException("The maxSize argument ("
					+ maxSize + ") is not a positive integer.");
		}
		this.maxSize = maxSize;
		ea = new LoggingEvent[maxSize];
		first = 0;
		last = 0;
		numElems = 0;
	}

	/**
	 * Add an <code>event</code> as the last event in the buffer.
	 */
	public void add(LoggingEvent event) {
		ea[last] = event;
		if (++last == maxSize)
			last = 0;

		if (numElems < maxSize)
			numElems++;
		else if (++first == maxSize)
			first = 0;
	}

	/**
	 * Get the <i>i</i>th oldest event currently in the buffer. If <em>i</em> is
	 * outside the range 0 to the number of elements currently in the buffer,
	 * then <code>null</code> is returned.
	 */
	public LoggingEvent get(int i) {
		if (i < 0 || i >= numElems)
			return null;

		return ea[(first + i) % maxSize];
	}

	public int getMaxSize() {
		return maxSize;
	}

	/**
	 * Get the oldest (first) element in the buffer. The oldest element is
	 * removed from the buffer.
	 */
	public LoggingEvent get() {
		LoggingEvent r = null;
		if (numElems > 0) {
			numElems--;
			r = ea[first];
			ea[first] = null;
			if (++first == maxSize)
				first = 0;
		}
		return r;
	}

	/**
	 * Get the number of elements in the buffer. This number is guaranteed to be
	 * in the range 0 to <code>maxSize</code> (inclusive).
	 */
	public int length() {
		return numElems;
	}

	/**
	 * Resize the cyclic buffer to <code>newSize</code>.
	 * 
	 * @throws IllegalArgumentException
	 *             if <code>newSize</code> is negative.
	 */
	public void resize(int newSize) {
		if (newSize < 0) {
			throw new IllegalArgumentException("Negative array size ["
					+ newSize + "] not allowed.");
		}
		if (newSize == numElems)
			return; // nothing to do

		LoggingEvent[] temp = new LoggingEvent[newSize];

		int loopLen = newSize < numElems ? newSize : numElems;

		for (int i = 0; i < loopLen; i++) {
			temp[i] = ea[first];
			ea[first] = null;
			if (++first == numElems)
				first = 0;
		}
		ea = temp;
		first = 0;
		numElems = loopLen;
		maxSize = newSize;
		if (loopLen == newSize) {
			last = 0;
		} else {
			last = loopLen;
		}
	}
}
